P. Ujic, F. de Oliveira Santos, M. Lewitowicz, L. Achouri, M. Assié, B. Bastin, C. Borcea, R. Borcea, A. Buta, A. Coc, G. De France, O. Kamalou, J. Kiener, A. Lepailleur, V. Meot, A. Pautrat, M. G. Saint Laurent, O. Sorlin, M. Stanoiu, V. Tatischef
The decay of $^{19}$O($\beta^-$) and $^{19}$Ne($\beta^+$) implanted in niobium in its superconducting and metallic phase was measured using purified radioactive beams produced by the SPIRAL/GANIL facility. Half-lives and branching ratios measured in the two phases are consistent within one-sigma error bar. This measurement casts strong doubts on the predicted strong electron screening in superconductor, the so-called superscreening. The measured difference in screening potential energy is 110(90) eV for $^{19}$Ne and 400(320) eV for $^{19}$O. Precise determinations of the half-lives were obtained for $^{19}$O: 26.476(9) s and $^{19}$Ne: 17.254(5) s.
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http://arxiv.org/abs/1212.3579
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